Alkyl 3-chloroanthranilates are useful intermediates in the manufacture of a variety of chemical products including agricultural chemicals: see, for example, U.S. Pat. No. 4,954,163.
The direct chlorination of anthranilates to the 3-chloro isomer has not been very successful. Chlorination of methyl anthranilate with molecular chlorine, for example, gives predominantly methyl 5-chloroanthranilate with substantial amounts of dichlorination. N-Chlorosuccinimide has been used as a chlorinating agent for various substrates but with very unpredictable results as to the product and by-product ratios obtained. The use of N-chlorosuccinimide to chlorinate aniline and N-alkyl or ring alkyl anilines has led to the production of p-chlorinated anilines or to mixtures of o- and p-chlorinated anilines; see, for example, N. Buu-Hoi, J. Chem. Soc, 2815 (1958); T. Chao, J. Org. Chem., 26, 1079 (1961); R. Neale, J. Org. Chem., 29, 3390 (1964): and D. Paul, J. Org. Chem., 41, 3170 (1976). Although some ortho chlorination is obtained, substantial amounts of para chlorination also prevail.
Because of this unpredictability with respect to electrophilic halogenations, other approaches to alkyl 3-chloroanthranilates are usually advocated. For example, U.S. Pat. No. 4,306,074 discloses the preparation of a mixture of alkyl 3-chloroanthranilate and alkyl 6-chloroanthranilate in a 3:1 ratio from 3-chlorophthalic anhydride by amination, Hofmann degradation and esterification. ##STR1## This procedure entails three discrete steps, not including separation of the resultant mixture, after chlorine has been introduced into the starting material. It would be desirable to have a process in which an alkyl 3-chloroanthranilate could be obtained in high proportion to other less desirable isomers directly from the corresponding alkyl anthranilate.